Well I have a 2009 Honda Accord Sedan and my power locks, power windows and power mirrors do not work. This was after I got my heater core replaced. Not sure what the issue is and neither does the mechanic that did the work. Any suggestions ?

You know the person who did the work is the one who most likely caused the issue, yes? That person should be responsible for the fix IMO.

Locks/windows/mirror controls all originate at the drivers master switch in the door, so it should be something related to its circuits

From a job like pulling the dash, I'd expect at least one of the harness junction connectors isn't fully seated and locked together (or missed completely), but there are an awful lot of those to choose from. Could be on the fusebox, could be in the kick panel, could be attached to the fuse box, could be one of the connectors that leads to the drivers door.

If the door panel was off, it could be the connector right on the master switch.

Mirrors seems like a simple circuit to start with, check fuses 13 and 16 in the dash fuse box, check all multi-wire connectors in the area, check the harnesses that leads toward the door hinges and disappears.